Ink is used in a number of ways by an inkjet printer throughout an inkjet printing process. While most of the ink used by the printer is dedicated to printing on media the desired documents, such as photographs and other textual and graphic documents, some ink must be used for maintenance purposes to maintain the health of the printer. For example, some ink may be necessarily used to initialize and service the print head in the printer, some ink is residual and cannot be removed for use by the printer to print documents, and some ink evaporates during the operation and life of the printer.
Accordingly, printing efficiency is reflected in the ratio of the amount of ink available to print documents on media (papers, labels, etc.) and the amount of ink the printer uses for printer maintenance. Printing efficiency is commonly measured by page yield, which is defined as the average number of pages a printer can print per ink cartridge, which stores a given or predefined amount of ink for printer use. Page yield is affected by various known factors, such as the content that is printed, how the end of life of an ink cartridge is determined, how much time passes between print jobs (e.g., continuous printing versus start-and-stop printing), etc.
Different tests may be used to calculate or measure the page yield. Some of the common tests include calculating page yields for continuous printing and for intermittent or start-and-stop printing. For example, it has been estimated that a common user of an inkjet printer typically performs start-and-stop print jobs, each job a few pages at a time, with hours and sometimes days between each job. With start-and-stop printing, a typical inkjet printer must frequently use some ink to keep its print nozzles clear and ink flowing smoothly. The amount of ink used for such maintenance varies with the model or type of printer and the manufacturer of the printer.
As known in the art, maintenance in an inkjet printer mainly involves the cleaning of the inkjet nozzles or pens on the printhead to prevent the blockage of such nozzles by dry ink. Typically, when the nozzles are not used for a print job, they are covered with a protective cap to prevent moisture evaporating from the nozzles, which can dry up and harden the ink in the nozzles. However, this capping or seal is not perfect, and moisture can still escape from the nozzles. To combat this dry-ink problem, an inkjet printer typically provides out-of-cap services and into-cap services to reapply moisture to the nozzles on the printhead. That is, every time a print job is issued to the printer, the nozzles on the printhead are uncapped, and an out-of-cap service is performed on the nozzles based on how long they were capped. Once the print job is complete, an into-cap service is performed on the nozzles before they are moved into the protective cap. Based on the amount of ink used during the print job, a mid-job service also may be performed.
Algorithms used to service and maintain the nozzles typically include a combination of spitting and wiping. In a spitting process, drops of ink are fired through each of the nozzles to clear or purge the nozzles of ink clogs or occlusions and to reapply moisture to the printhead. The waste ink is collected at a spitting reservoir in the printer known as the “spittoon.” In a wiping process, a flexible wiper (e.g., a rubber wiper blade) is swept across the printhead to spread the moisture evenly and remove ink residue as well as any dust or other debris that has collected on the printhead. The wiping process may be performed after spitting, uncapping, or occasionally during printing.
Because of more frequent maintenance of the inkjet printer for start-and-stop printing, page yields measured for typical start-and-stop printing are lower than those measured for continuous printing. It has been found that a page yield by a typical inkjet printer for continuous printing is as much as 150% more than a page yield for start-and-stop printing by the same printer. Prior solutions attempted to improve the page yield for start-and-stop printing by providing schemes wherein the inkjet nozzles or pens are left uncapped for a period of time after each print job in anticipation of another print job. Thus, to save ink, out-of-cap and into-cap services need not be performed on the printhead in between jobs. For example, after a print job is complete, the inkjet nozzles are left uncapped for two seconds in anticipation of another print job, after which the nozzles are capped. However, even if two print jobs are issued consecutively, there remains the possibility that the second print job may not meet the two-second deadline due to its size. Consequently, ink will be expended to perform both an into-cap service on the inkjet nozzles before they are capped and an out-of-cap service when they are uncapped for the second print job.
Accordingly, there is a desire to improve the printing efficiency of inkjet printers for both continuous and start-and-stop printing, so that the printer ink is maximally used for actual print jobs to print documents on media and minimally used to sufficiently maintain a reliable printing system that continues to deliver a desired print quality.